Mechanical damage may be caused when a shaft turning at a high rate of rpm's is disengaged and, before it has slowed down is re-engaged or shifted to the other direction of rotation. For example, if the operator for a drive shaft mechanism is accidentally and suddenly thrown into reverse while the machine is running in a forward direction at a relatively high rpm, the sudden shifting will place stresses and strains upon the drive shaft and operating mechanism causing damage. The present invention is of an electrical monitoring and safety device for an electrical coil shifting circuit to guard against such damage. The device provides protection to the mechanical drive mechanism associated with the coil shifting circuits, one a forward circuit and the other a rearward circuit, causing a rapid shut-down of the shifting circuits by the monitoring device. The main purpose of the monitoring device is to isolate the mechanical portion of a drive system whenever there is an electrical malfunction either by loss of applied voltage or ground return.
For example, in a situation where a drive shaft is rotating at a high rpm and the drive means is disengaged, if it is re-engaged before the rpm's are reduced below a certain level, damage is likely to occur. With the present invention, the rpm's are monitored to lock out the shifting circuit, so that it will not re-engage until the rpm's have been lowered below a predetermined level, one chosen at which damage is not likely to occur.
It is, accordingly, an object of this invention to provide a monitor and safety device for a coil shifting circuit.